MySQL入門（二）：基礎練習

sqlzoo習題練習：SELECT from world

習題鏈接：http://sqlzoo.net/wiki/SELECT_from_WORLD_Tutorial

下面為SELECT from world習題內容：

--#1/*Read the notes about this table. Observe the result of running a simple SQL command.*/SELECT name, continent, populationFROM world--#2/*How to use WHERE to filter records.Show the name for the countries that have a population of at least 200 million. 200 million is 200000000, there are eight zeros.*/SELECT nameFROM worldWHERE population>=200000000--#3/*Give the name and the per capita GDP for those countries with a population of at least 200 million.*/SELECT name, gdp/populationFROM worldWHERE population >= 200000000--#4/*Show the name and population in millions for the countries of the continent South America. Divide the population by 1000000 to get population in millions.*/SELECT name, population/1000000FROM worldWHERE continent = South America--#5/*Show the name and population for France, Germany, Italy*/SELECT name, populationFROM worldWHERE name in (France, Germany, Italy)--#6/*Show the countries which have a name that includes the word United*/SELECT nameFROM worldWHERE name LIKE %united%--#7/*Two ways to be big: A country is big if it has an area of more than 3 million sq km or it has a population of more than 250 million.Show the countries that are big by area or big by population. Show name, population and area.*/SELECT name, population, areaFROM worldWHERE area > 3000000 OR population > 250000000--#8/*Exclusive OR (XOR). Show the countries that are big by area or big by population but not both. Show name, population and area. Australia has a big area but a small population, it should be included. Indonesia has a big population but a small area, it should be included. China has a big population and big area, it should be excluded. United Kingdom has a small population and a small area, it should be excluded.*/SELECT name, population, areaFROM worldWHERE (area > 3000000 AND population < 250000000) OR (area < 3000000 and population > 250000000)--#9/*Show the name and population in millions and the GDP in billions for the countries of the continent South America. Use the ROUND function to show the values to two decimal places.For South America show population in millions and GDP in billions to 2 decimal places.*/SELECT name, ROUND(population/1000000,2), ROUND(gdp/1000000000, 2)FROM worldWHERE continent = South America--#10/*Show the per-capita GDP for those countries with a GDP of at least one trillion (1000000000000; that is 12 zeros). Round this value to the nearest 1000.Show per-capita GDP for the trillion dollar countries to the nearest $1000.*/SELECT name, ROUND(gdp/population, -3)FROM worldWHERE gdp >= 1000000000000--#11/*Greece has capital Athens.Each of the strings Greece, and Athens has 6 characters.Show the name and capital where the name and the capital have the same number of characters.You can use the LENGTH function to find the number of characters in a string*/SELECT name, capitalFROM worldWHERE LENGTH(name) = LENGTH(capital)--#12/*The capital of Sweden is Stockholm. Both words start with the letter S.Show the name and the capital where the first letters of each match. Dont include countries where the name and the capital are the same word.You can use the function LEFT to isolate the first character.You can use <> as the NOT EQUALS operator.*/SELECT name, capitalFROM worldWHERE (LEFT(name,1) = LEFT(capital,1)) AND (name <> capital)

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